Process for roasting ores



Feb. 15,` 1938. E. J. MULLEN 2,108,592

Y PROCESS'FOR ROASTING CRES Filed Dec. 25, l1955 s sheets-sheet 1 am M4ATTORNEY Feb. 15, l1938. E. J. MULLEN PROCESS FOR ROASTING ORES FiledDec. 23, 1935 3 Sheets-Sheet 2 INVENTOR BY? I:

' ATTORNEY Feb. 15, 1938. E. .1. MULLEN' 2,108,592

PROCESS F'oR ROASTING GRES' Filed Dec. 23, 1955 5 sheets-sheet sATTORNEY PROCESS FUR ROAS'HING DRES Edwin l. Mullen, New helle,

to General Chemical Company,

N. Y., assigner rNew York,

N. Y., a corporation of New York Application December 23, 1935; SerialNo. 55,808

Claims.

This invention is directed to methods for roasting sulfide ores todesulfurize the same and to produce sulfur dioxide for use in themanufacture of sulfuric acid, or for any other purposes desired.

To a substantial extent, present practice in roasting of sulfldes suchas pyrites includes use of mechanically operated multiple hearthfurnaces., such for example as the well-known MacDougall, Herreshoff andWedge burners. As distinguished from' the bed or hearth roastingoperation of these burners, it has been suggested to roast nely dividedsuldes while in gaseous suspension. Suspension roasting processes suchas shown for example in Burgoyne and Cordy U. S. Patent No. 1,758,188 ofMay 13, 1930 have been developed largely because of availability inrecent years of supplies of suldes, such as flotation concentrates,sufficiently finely divided to permit roasting by suspension methods.

In the present state of the art of producing Sulfur dioxide from'sulfides, it may be said that probably the major portion of the sulfurdioxide utilized in the manufacture of sulfur trioxide by the contactprocess is obtained by roasting what is known as pyrites smalls. Theusual run-ofpile of pyrites smalls has been crushed so that 100% passesa half inch screen. A substantial portion of an ore of this type issuiiciently nely divided for suspension roasting if separated from thecoarser material, although a large portion of the small's, in many casesthe major portion, comprises ore too coarse for suspension roasting ubypresent methods. In the present specification, smalls is used in ageneric sense to dene a run-of-pile ore containing some ore fine enoughfor suspension roasting and some ore too coarse for suspension roasting.The term coarse is used to denote ore of too large particle size forroasting by suspension methods, and nes is utilized to designate sulfideores suciently finely divided' to permit roasting by suspension methods.

Since smalls usually contain a substantial portion' of coarse ore, thesmalls have'heretofore been roasted as in a multi-hearth roaster orground to a sufcient degree of neness to permit suspension roasting.While multi-hearth furnaces such as the Wedge and Herreshoi burnersprovide eiective roasting, use of burners of this type is objectionableprincipally on account of the low capacity per unit of apparatus perunit of time and because the` complicated constructiony and operationinvolves substantial initial and maintenance expense. On the other hand,grinding of smalls to such an extent that all of the ore may be roastedin gaseous suspension is not desirable since in many instances grindingcosts are prohibitive.

The present invention aims to provide a method for roasting a sulde ore,such as pyrites smalls, by means of which method the ore, withoutfurther grinding, may be roasted in a way much more eiilciently than ina standard multi-hearth burner. 'Another object of the invention is toprovide apparatus for carrying out the improved process.

The nature of the invention and the objects and advantages thereof maybe fully understood from consideration of the following descriptiontaken in connection with the accompanying, drawings in which- Fig. 1 isa vertical longitudinal section of a burner in which the improvedprocess may be carried out;

Fig. 2 is a horizontal section taken approximately on theline 2-2 ofFig. 1;

Fig. 3 is an enlarged vertical section ferred type of fines injector;and

Fig. 4 is a vertical longitudinal section of a modied burner. y A

Referring to Fig. 1, I0 designates a burner comprising a steel shell orcasing I l within which is placed the furnace lining l2 constructed ofsuitable refractory material, such as rebrick and defining a roastingchamber It of circular, horizontal cross-section. The upper part of thecombustion chamber is closed off by a crown l5 the top side of whichforms a drying or preheating hearth l1. The shell ll projects upwardlybeyond crown l5 and carries a steel framework i8 which in turn supportsore feeding and rabbling mechanism for the drying hearth. The surface ofhearth I'l is slightly cone-shaped and slopes downwardly toward theshell of the burner. Lying above the hearth are rabble arms i9 havingdownwardly projecting plows pitched to work suldes gradually toward thecircumference of the drying hearth. Arms i9 are rotated by motor 22through shaft 23 supported in bearings so as to maintain the lower endsof plows 20 spaced with respect to the surface of hearth ll. An ore bin2t, mounted on framework I8, discharges ore of a preonto a platform 25from which the smalls are intermittently dropped to the center of dryinghearth ll by a sweep 2l rotating with shaft 23.

Attached to shell I l by brackets notshown are hoppers t0 covered bysloping screens 3l. Cut through shell Ill and also through the upperedge of lining l2 are downwardly sloping passages or conduits :itthrough which-smalls are passed from hearth Il yto screens 3l.l It willbe understood 2 the number of conduits 34 and hoppers 30 and 32 used inconnection with the burner corresponds with however many ore injectors40 may be employed. On rotation of rabble arms i9, the sulfide ore isgradually fed through openings 34 onto the screens 3| which separate thecoarse ore and the nes, the fines collecting in hoppers 30 and thecoarse ore in hoppers 32. Hoppers 30 discharge fines into injector feedpipes 35 having at their lower ends any suitable means such as slidevalves 35 for controlling flow of fines out of the lower ends of pipes35.

The nes injectors 40 comprise principally an elongated pipe section ornozzle 38 constituting a fines inlet conduit. A pipe 39, carrying on theupper end a funnel 4|, is arranged to feed nes into the lower end ofnozzle 38. Air or other gas used to inject the fines into the burner issupplied from a bustle 42, surrounding the lower end of the burner, andconnected to a. blower or other source of air through pipe 43. Adjacenteach injector 40, pipe 42 is provided with an air outlet nipple 44having a control valve 45. Numeral 46 representsl a flexible hoseconnection attached at one end to nipple 44 and at the other end to jet41. The lower end of nozzle 38 is provided with a clean-out plug 50.Each injector unit, comprising a nozzle 38, feed pipe 39, and funnel 4|,may be supported by a suitable bracket not shown in such a Way as topermit adjustment of the angle between the axes of nozzles 38 and thehorizontal and also the angle between the axes of the nozzles 38 and theradii of the combustion chamber. The burner may be provided with anysuitable number of injectors, and in the embodiment illustrated, sixinjectors 40 are employed.

The bottom of the combustion chamber is formed by a slightly cone-shapedhearth 60 sloping downwardly toward the shell of the burner. Spacedabout the periphery of the hearth are outlets 6| through which cinder isdischarged by means of pipes 64 into a chamber 66 from which the cindermay be removed as by a conveyor 61, without permitting gas to escapefrom the combustion chamber.

Located in the bottom of the combustion chamber are rabble arms 10 and1|, shown in elevation in Fig. 1 and in plan in Fig. 2, carried on theupper end of a hollow shaft 14 supported at the base by a bearing 15.Shaft 14 passes through the center of hearth 60 and is made as at 11with a suitable joint to prevent gas escape from the combustion chamber.Arms 10 and 1| are equipped on the lower side with plows 80 pitched soas to gradually work solids from the center of the hearth outwardly todischarge outlets 8|. It will be understood arms 10 and 1| are attachedto the upper end of shaft 14 high enough to hold the lower ends of plows80 spaced suflciently above the surface of hearth 60 to permitmaintenance thereon of a bed of roasting ore and/or cinder of anydesired degree of thickness.

Referring to Fig. 2, it will be seen hollow arm 10 is made with avertical longitudinal partition 84 forming air passages 85 and 86.Passage 85 communicates at the inner end with hollow shaft 14 and at theouter end, as at 88, with the outer end of passage 86 terminated by adead end 89. The lower side of arm 10 is provided with a series of ports9|, opening into passage 86, into which ports are set air jets 92positioned to cause air discharged through the jets to impinge at anangle upon the surface of a bed of ore and/or the combustion chambercinder lying on hearth 00. Arm 1| is made in the same way as arm 10.

Additional quantities of air are supplied to the lower end of thecombustion chamber through hollow radial pipes or arms 95 opening at oneend into shaft 14 and at the other end into a circular air distributingpipe 91. From Fig. 2, it will be seen radial pipes 95 and circular pipe91 are provided with air jets 98 positioned similarly to air jets 92carried by rabble arms 10 and 1|. The upper end of shaft 14 is alsoprovided with a plurality of circumferentially spaced air jets 99 bymeans of which air may be supplied to the surface of the bed immediatelysurrounding the shaft. In operation, shaft 14 and the associated rabblearms 10 and 1|, radial pipes 95 and circular distributing pipe 91 arerotated in the direction of arrow in Fig. 2 through pinion |02 and gearH04 from a source of power not shown. In the apparatus illustrated inFig. 1 all or the greater part of the air used in the roasting operationis introduced into the lower end of the combustion chamber through shaft14 to which air is furnished from a housing surrounding the shaft andconnected to an air pipe |00 to which air is supplied by a blower notshown. The balance of the air required in the combustion chamber may bedrawn in through one or more ports |08 (Fig. 2) in the lower walls.Ports |08 may be provided with removable covers |09.

As shown by Fig. 1, carried byarms and 1| is a coarse ore collector orfunnel ||0 having an outlet opening in the bottom appreciably larger indiameter than the upper end ||2 of shaft 14. Collector ||0 may be madeof heatresistant material, or may be provided with an air jacket ||5communicating at the lower end by connections not shown with hollow arms10 and 1| and having a plurality of circumferential outlets ||1 at theupper edge through which air is discharged into the combustion chamberand utilized in the roasting reaction.

Hoppers 32 supply coarse ore into coarse ore feed pipes |20 which passthrough the burner wall into the combustion chamber I4 and discharge oreonto the upper surface of collector l0. Those portions of pipes |20within the combustion chamber |4 may be cooled by suitable air or waterjacketing. Coarse ore runs from the surface of collector ||0 throughopening onto the approximate center of hearth 60.

A gas main |25, for withdrawing gaseous products of combustion from theburner, opens into I4 at a point just below crown I5. v

In the modified form of burner shown in Fig. 4

the construction is substantially the same as illustrated in Fig. 1except that the injector nozzles |30 pass through the burner walls at apoint just below crown |3|. Nozzles |30 are pitched at a considerablylower angle than nozzles 38 of Fig. l, and as in the case of nozzles 38may be made so as to permit some limited adjustment of the nozzlebetween the axes of nozzles |30 and the horizontal and/or radial plane.The fines from hoppers |32 are fed through short pipes |33, havingcontrol valves |35, into the lower ends of nozzles |30. Flow of air intothe nozzles through jets |36 may be regulated by valves |31.

Provision is made forA introducing air into the top of the combustionchamber |42 through a series of circumferentially spaced ports |43 eachof which communicates with a pipe |44 connected at the outer end with anair bustle |45. Air is introduced into bustle |45 through an' inlet pipeMii, having a control valve Ill'i, and connected to a blower not shown.Gaseous products of combustion are withdrawn through a gas main I50opening into the lower end of the combustion chamber.

The invention is applicable to the roasting of sulfide ores such as ironpyrites, pyrrhotite, zinc sulfide or arsenopyrite, but for conveniencethe' operation of the process will be described in connection with theroasting of iron pyrites smalls. In the following specific example,given to -illustrate one preferred embodiment of the invention, it maybe assumed the ore referred to is a run-of-pile or pyrites smalls ore,100% passing a half inch screen and containing about 50% coarse oreinsufliciently finely divided for suspension roasting, and about 50%nes/(e. g. 30 mesh or finer) of such size as to permit roasting insuspension.

A supply of pyrites smalls is maintained in bin 24 by suitable conveyoror elevator, not shown.

Before roasting is begun, combustion chamber I4 is` preheated totemperatures above the ignition point of the ore to be roasted, as byoil burners inserted through conveniently located work-holes not shown.When the desired degree of preheat is obtained, motor 22 is started, andrabble arms I9 and sweep 21 may be rotated at a rate of say onerevolution in two minutes. Smalls run con-` tinuously out of bin 24 ontoplatform 25, and on each revolution of shaft 23 a regulated quantity ofore is swept off the platform to approximately the centerof dryinghearth I'I. During rotation of arms I9, the sulfide smalls are graduallyworked across the surface of hearth Il and into the several passages 34,each of which discharges smalls onto a screen 3| which may for examplebe about 30 mesh. The lines, about 30 mesh and finer, collect in hoppers30, and the coarse'ore runs into and is collected in hoppers 32. Durling movement of the smalls over hearth I'l, the

fines and the coarse ore may be preheated as a rule to about 250 F. andgenerally not in excess of about 40o-500 F.

Referring first more particularly to the suspension roasting phase ofthe process, the dry or dry and partly preheatediines run from hoppers3l) into feed pipes 35. Valves 3B in pipes 35 are adjusted so thatsubstantially steady streams of nes run into the lower ends of nozzles38 through funnels Ill and pipes 39. Air, steam, or other gas, notadversely affecting oxidation of the sulfide, may be employed to chargethe fines into the combustion chamber. is preferred to employ air whichmay be admitted to they lower ends of nozzles 38 through jets diatpressures of, for example, about 5 pounds per square inch.

The angle of the axes of nozzles with the horizontal is dependent uponthe size and type of combustion chamber. The angle `of the axes ofnozzles 38, the amount of lines fed into the injectors through pipes 30,and the air pressure in jets di, adjusted by valves t5, are allregulated with respect to the size of the particular roasting chamber sothatthe ore-particles from `each injector rise through the combustionchamber,

walls. Referring to Fig. 1, dotted line IE5 in.-

dicates the approximate path of travel of a fines particle of averagesize introducedthrough the injector'on the left side of the burner.

'Since two or more injectors (in the present instance six) arepreferably employed, contacting of fines particles constituting theindividual streams fed into the combustion chamber by the separateinjectors, breaks up the normal paths of travel of the ore particles sothat the drop of the fines from the top to the bottom of the combustionchamber is a substantially straight line fall, or one at a high angle.With respect to the path of travel of fines through the combustionchamber, the fines particles move upwardly at an angle-somewhat lessthan the pitch of nozzles 38, to an elevation just below crown I5 where,by commingling of the particles of several in. dividual streams offines, a relatively uniform dispersion is formed over a major portion ofthe upper end of the combustion chamber. The particles then settle inmore or less straight lines, at a rate approaching that induced bygravity, toward the hearth in the bottom of the combustion chamber. Inthis way, the fines are caused to pass over substantially the longestpossible path of travel in any particular combustion chamber. During thelatter part of the upward travel of the fines, the rate of verticalmovement thereof rapidly decreases to zero, and thereafter, duz"- ingthe initial part of the descent of the nes, therate of downward mouementof the fines is relatively small. Hence, while passing upwardly anddownwardly through the upper zone of the combustion chamber, the averagerate of move- For this purpose, it

ment of the nes is low, and this slow rate of travel increases the timethe particles are in the roasting atmosphere, thereby giving arelatively long time for the suspension roasting to proceed, thuspermitting use of a roasting chamber of relatively short verticaldimension, and making possible a high capacity of the burner.

The major portion of the total quantity of air, or other oxidizing gas,necessary to Support suspension roasting of the fines and hearthroasting of the coarse ore is introduced into the bottom of thecombustion chamber through shaft lt, arms l0, il, 95, and pipe 9i. Whereair is employed for injecting the nes through nozzles 38, usuallysubstantially less than about 10% of the total air required foroxidation would ordinarily be introduced thru air jets M. Hence, it maybe considered that in this example substantially all o-f the air neededis introduced into the bottom of the combustion chamber through shaftlli. In the specic embodiment of the in? vention described, thecombustion chamber maybe about 16 feet high, and the diameter of thecombustion chamber may be about the same. Whilesuch particularproportions of the roasting chamber are satisfactory, it is to beunderstood the diameter of the chamber may in some instancesadvantageously exceedthe'height by a substantial amount, and may also besomewhat less than the height. Since the combustion chamber preferablyhas a large diameter per unit of volume, the velocity of the upwardlyflowing gas stream may be held low thus avoiding undue disturbance ofmovement of fines in the sov 1lcombustion chamber above the hearth.Further, where the proportions of the combustion chamber are about asstated, the loss of heat to the outside atmosphere is minimizedpermitting the inner wall area to efficiently supply radiant heat to theroasting of coarse ore taking place on the hearth 6U. Under someoperating conditions it may be desirable to provide for introduction ofan appreciable fraction of the air required for combustion through oneor more of the ports |08 in the burner wall. It will be understood thatthe burner as a whole operates under minus pressure induced by a fan ingas line |25.

The sulfide fines, dried and more or less preheated, are injected intothe lower end of the combustion chamber and into an atmosphererelatively rich in oxygen.- Heating of the upwardly moving finesparticles to ignition temperature takes place rapidly, owing to theabsorption of radiant'heat from the suspension zone and from the coarseore roasting on the hearth.

Following ignition, the fines rise to approximately the top of thecombustion chamber, the temperature of the particles increasing becauseof rapidly progressing roasting. The temperature of the roastingoperation as a whole may `Vbe around l800 F. and the temperature of thegases in the top of the roasting chamber, on entering outlet |25, may beabout 1800-2000 F.

At the uppermost point of travel of the fines, a relatively uniformdistribution of partially roasted fines particles is formed over themajor portion of the upper end of the combustion zone and the downwardmovement of the particles begins.

The fines thereafter drop through the combustion chamber at a rateapproaching that of similar particles falling under since operations arepreferably so conducted that the velocity of the stream of gas risingthrough the combustion chamber is not sufficient to interfere with thefree gravity fall of the fines. Because of the angular pitch of nozzles38, and other above-noted control conditions, fines particles during theupward movement are not thrown against the walls of the roastingchamber, and thus contact of fines with the hot walls of the combustionchamber is avoided when the fines are in a state conducive to. scarring.As the downward kflow of the fines is in substantially straight lines orat a high angle, subsequent contact of fines with the walls of thecombustion chamber is avoided, thus further preventing conditions underwhich scarring of the burner might take place. The relatively coolcondition of feed pipes |20 seems to prevent accumulation of scarthereon.

At the time downward movement of the fines particles begins, roasting iswell under way, but because of the decreasing sulfur content of 'thefines, to complete roasting, it is desirable to cause the finesparticles to pass through an atmosphere increasingly rich in oxygen. Inthe operation of the present process, this conditon is present. Althoughthe upwardly flowing gas stream contains all the -sulfur dioxide formedby roasting the coarse ore on hearth 60, itwill be understood that withrespect to the amount of oxygen needed to effect roasting of the fines,the fines roasting atmosphere is richest in oxygen at the bottom of thecombustion chamber and decreases toward the top on account ofconsumption of oxygen in oxidation of sulfur and iron of the fines.During fall through the combustion chamber, roasting of the influence ofgravityf fines is completed, and finely divided free-flowing iron oxidecinder falls onto the bed of coarse ore on the hearth 60. The result ofcompletion of roasting of a given quantity of sulfide fines isproduction of a given amount of sulfur dioxide and iron oxide cinder,and generation of a substantial amount of heat which ls made availableas radiant heat reflected back into the combustion zone by the burnerwalls.

In accordance with the preferred embodiment of the present invention,while the fines contained in any given quantity of smalls are beingroasted in suspension as above described, during a given interval oftime, (the term time interval being used to designate the interval oftime required to react the total quantity of fines contained ina givenquantity of smalls as distinguished from the time interval required toflash roast a given fines particle) the coarse ore contained in such,quantity of smalls is being roasted simultaneously in a bed roastingoperation with the ald of the high temperatures generated by thesuspension roasting of the fines.

As indicated, the suspension roasting operation develops temperatures inthe combustion chamber of around 18002000 F. In the process of theinvention, these temperatures are utilized to effect rapid and efficientroasting of the coarse ore fed into the combustion chamber through pipes|20. In accordance with the invention, it has been found that when abody of smalls, containing not too great aproportion of coarse ore, isintroduced into a combustion zone and the coarse ore component of thesmalls is suddenly subjected to relatively high temperatures, preferablynot less than about 1300 F., the coarse ore is converted to a conditionsuch as to facilitate substantially complete roasting of the coarse orein a bed roasting operation simultaneously with the suspension roastingof the fines contained in any given quantity of smalls.

When proceeding in accordance with the preferred process of theinvention, the coarse ore which may be preheated to temperatures ofaround 250 F. and not generally in excess of about 40G-500 F. is fedfrom hoppers 32 into the combustion chamber through pipes |20, andtherate of introduction is regulated by valves |2|. The coarse ore runs offcollector ||0 onto the center of hearth 60. Owing to the high combustionchamber temperatures, which are preferably not less than about 1300 F.,and are usually much in excess of about 1300* F., the coarse oreparticles are very suddenly subjected to high temperatures, andexperience indicates the loosely combined sulfur of the coarse ore ispractically instantaneously volatilized on introduction of the coarsecre into the high temperature atmosphere of the combustion zone, and onaccount of such sudden exposure to high temperatures and consequentdifferential expansion strains are set up in the coarse ore particlesthus disrupting and converting the ore particles to a porous condition.In acwrdance with the invention, it has been found that when the coarseore is introduced into the combustion zone where temperatures not lessthan about 1300 F. prevail, the resulting differential expansion andrapid volatilization of loosely combined sulfur appears to exert, withinthe lumps of coarse ore, explosive forceswhich open up the ore,rendering the particles porous and permitting rapid reaction of oxygenwith the remaining sulfur contained in the coarse ore. The suddensubjection of the om to high temperatures referred to should bedistinguished from alcance .,volatilization of the loosely combinedsulfur, the

coarse ore on hearth 60 rapidly reaches'temperatures around 1800 E'. byabsorption of heat from the suspension zone and from the combustion ofthe sulfur and iron contained in the coarse ore on the hearth.

It will be understood the amount of air (preheatedif desired) introducedthrough the hollow shaft 14, rabble arms 10 and 1|, radial arms 95 andthe circular distribution pipe 91 (and through ports |08 if utilized) isregulated so as to provide in the combustion chamber a sufficientquantity of oxygen to oxidize the sulfur and iron contained in thecoarse material on the hearth 60 and also to `supply most of the oxygenrequiredto effect oxidation of the fines which are roasted while insuspension. As is shown in Fig. 2, air is supplied to the bed of coarseore relatively uniformly overthe entire surface. As the amount of airpassing through the air jets includes most of that needed in thesuspension roasting of the nes, it will be seen that an excess of air isdistributed over the coarse ore bed. Uniform distribution of air and thepresence of plenty of air in conjunction with utilization of the hightemperatures developed by the suspension roasting operation effectsrapid oxidation of the coarse ore as the latter is moved outwardly overthe hearth 60 toward the burner periphery. In the specic example underdiscussion in which the diameter of the combustion chamber is around 16feet, the pitch of plows 80 and the rate of rotation of rabble arms 10and 1| may be adjusted so as to move the coarse particles over thehearth in about two hours. Cinder discharged through conduit `|54 isfree-owing and is substantially all magnetic yiron oxide. When carryingout the process as described with pyrites smalls of the type mentioned,satisfactory desulfurization of both nes and coarse ore may be obtainedand an 8 to 12% sulfur dioxide gas produced which is ywithdrawn throughoutlet |25,

Although it is preferred to conduct the suspension roasting phase of theprocess in the manner described in connection with the burner-of Fig. 1,this part of the process may be carried out in other ways. For example,in the burner of Fig. 4, the nes are roasted in aco-current roastingoperation.

The nes are fed from hoppers |32 into the upper end of a combustionchamber through nozzles |30 which may be upwardlyinclined'at an angle ofabout 25% to the horizontal. Dispersion of nes in the roasting chamberisnot dependent upon any particular degree of inclination of the nozzles|30 which may be horizontally disposed if desired. However, to securebest disperson of the nes in the combustion chamber andrmostsatisfactory roasting, it is not desired to feedthe ore kinto theroasting chamber in such a way that the` initial travel of the fineswill `be downward. The nes are charged into the combustion chamber byair introduced into' the injector through jet |36., Air pressure in jets|36 should'be preferably such as to cause'a considerable portion of thenes particles to travel approximately 1% of the way across thecombustion chamber. Although desirable to cause substantial portions ofthe fines to move a relatively `large distance horizontally across thecombustion chamber, the injectors should be so operated that lines fromone injector do not strike the opposite wall of the combustion chamber.When proceeding as indicated, there is formed within Ithe combustionchamber approximately at or slightly below the level of the inlet endsof nozzles |30`a relatively evenly distributed dispersion of sulfidenes, and as the number of lines particles striking the hot walls in theupper end of the combustion zone is negligible, troublesome scarformation on the walls of the roasting chambeiis avoided.

Owing to the relatively extensive horizontaltravel of the nes particlesin the upper end of the combustion chamber following injection, the

. particles become rapidly preheated to such an extent that about thetime the particles begin to descend through the combustion chamber theignition temperature'is reached and ore particles ignite. In the upperend of the combustion vchamber the feebly combined atom of sulfurdistills oi and is oxidized to sulfur dioxide. 'Ihe suspended particlesdrop, at a rate about or approaching that induced by gravity, and as thenes particles fall through the combustion chamber roasting proceedsrapidly.

The amount of air introduced into combustion chamber |42'through thehollow shaft, rabble arms and the air distributing arms is only aboutthat which is necessary to supply oxygen enough to oxidize the sulfurand iron of the coarse ore on hearth |49. The amount of air needed tosupply oxygen enough to support oxidation of' the nes roasted insuspension is introduced through the ports |43 and may be preheated ifdesired. 'Ihe air thus fed into the top of the combustion chamber may beregulated by valve |41 in inlet pipe |46, and passes downwardly throughthe combustion chamber co-current with the nes. The hearth roasting ofthe coarse ore is carried out as previously described. The gaseousproducts of combustion formed by roasting of the nes in suspension andby roasting of the coarse ore on hearth |40 are withdrawn through pipe|50 opening into the combustion chamber at a point a short distanceabove the hearth.

roasting of the .coarse ore of such body of smalls.

It will be understood the quantities of coarse ore and nes need not beobtained by screening a given body of smalls, but may be obtained fromdiierent sources if desired, that is the nes and the coarse ore may beobtained from different sources.

It will also be appreciated lthe process of thev invention is sufcientlyexible to permit change in control conditions sucient to handle smallscontaining variable proportions of nes and coarse ore. For example',when smalls'contain 'an excessive portion of fines, coarse ore fromanother source may be ladded to maintain the operations at maximumcapacity. Theprocess of the invention may also be employed to advantageinv roasting 'of smalls containing' a major portion of coarse ore andaminor portion of nes. In view of the relatively high temperaturesdeveloped by suspension roasting of fines, smalls containing coarse oreand fines in the Weight proportion of about approximately :40 may behandled in the process without utilization of heat other than thatdeveloped by the roasting operation itself, and in the preferredembodiment of the process, it is preferred to use smalls containing notless than about 40% by weight of fines. If a situation should arise inwhich the amount of fines contained in a particular body of smalls isinsuicient to supply heat enough when roasted in suspension to effectrapid roasting of the coarse ore, further heat units may be introducedinto the combustion chamber. For example, a desired amount of iines fromanother source may be added to the nes contained in the smalls. Further,pulverized or atomized combustible materials such as sulfur may be mixedwith and blown into the combustion chamber along with the fines, or acombustible gas may be used to inject the fines, or a combination ofboth. In this way the amount of heat generated in the upper part of thecombustion chamber may be regulated to supply whatever additional heatmay be needed.

Alternatively, a fraction of coarse ore may be separated, crushed andcombined with the smalls supplied to hearth I1. In my co-pendingapplication Serial No. 55,809, led December 23, 1935, I' have describeda process adapted to roast metal sulfide smalls containing a relativelysmall portion of fines.

The invention presents several substantial operating advantages. Forexample, when working with pyrites smalls passing a half inch screen asmentioned, it would ordinarily be necessary to roast this type of or'ein a multi-hearth burner or go to the expense of grinding the ore to asufficient degree of neness to permit roasting by suspension methods. Inaccordance with the present invention an ore of this kind may be roastedusually without further grinding, in a way much more ecient than couldbe accomplished in a. multi-hearth roaster.l For example, the capacityof burners of this type described in the application may be about 4times that of a hearth roaster of similar size.

In the present specification and claims, the expression bed or hearthroasting is used to designate that type of roasting in which (asdistinguished from suspensionroasting) the ore particles constitute amore or less continuous body but not necessarily in the form of arelatively thin layer on a horizontal'hearth.

I claim:

1. The method of roasting coarse metal sulde ore and metal sulfide fineswhich comprises introducing the nes into a combustion zone so as" toform in the combustion zone a suspension of the nnes in oxidizing gas,substantially completely.

roasting the fines while in suspension in the oxidizing gas therebyproducing sulfur dioxide gas and creating high temperatures, forming abed of the coarse ore, roasting the coarse ore, under intluence of thehigh temperatures developed by the suspension roasting of the nes, underconditions to substantially completely roast the coarse ore fand toproduce sulfur dioxide, and recovering sulfur dioxide.

2. The method of roasting coarse metal suliide ore and metal suliidefines which comprises introducing the nes into a combustion zone so asto form in the combustion zone a suspension of the rines in oxidizinggas, roasting the nes in suspension in oxidizing gas while passing themies downwardly through the combustion zone thereby substantiallycompletely roasting the nes while in suspension and producing sulfurdioxide and creating high temperatures, introducing the coarse ore intothe bottom of the combustion zone, forming in the bottom of thecombustion zone a bed of the coarse ore, roasting the coarse ore in thecombustion zone, under direct influence of the high temperaturesdeveloped by the suspension roasting of the nes and while moving thecoarse ore slowly through the combustion zone, under conditions tosubstantially completely roast the coarse ore and to produce sulfurdioxide and metal oxide cinder, withdrawing sulfur dioxide from thecombustion zone, and discharging cinder from the bottom of thecombustion zone.

3. In the roasting, by a method involving bed roasting of the coarse oreand suspension roasting of fmes, of a quantity of metal sulde coarse oreand a quantity of metal sulde fines in amount such lthat when roasted insuspension suiliciently high temperatures are created to effectsimultaneous roasting of the coarse ore, the steps comprisingintroducing the fines into a combustion zone, forming in the combustionzone a suspension of the nes in oxidizing gas, roasting the fines whilein suspension in the oxidizing gas thereby producing sulfur dioxide gasand creating high temperatures, forming a bed of the coarse ore,substantially completely roasting the coarse ore, under inuence of thehigh temperatures developed by the suspension roasting of the fines, toproduce sulfur dioxide' gas, and recovering sulfur dioxide gas.

4. In the roasting, by a method involving bed roasting of the coarse oreand suspension roasting of the nes, of a quantity of metal sulfidecoarse ore and a quantity of sulde nes in amount such that when roastedin suspension sufficiently high temperatures are created to effectsimultaneous roasting of the coarse ore, the steps comprisingintroducing the fines into a combustion zone, roasting the fines insuspension in oxidizing gas while passing nes downwardly through thecombustion zone thereby producing sulfur dioxide gas and metal oxidecinder and creating high temperatures, introducing the coarse ore intothe bottom of the combustion zone, forming in the bottom of thecombustion zone a bed of the coarse ore, substantially completelyroasting the coarse ore in the said combustion zone, under directiniiuence of the high temperatures developed by the suspension roastingof the fines and while moving the coarse ore particles slowly throughthe combustion zone to produce sulfur dioxide gas and metal oxidecinder, withdrawing sulfur dioxide gas from the combustion Zone, anddischarging cinder from the bottom of the combustion zone.

5. 'I'he method of roasting metal sulde smalls containing coarse suldeore and sulde fines which comprises separating the coarse ore .and therines, introducing the coarse ore and the nes into a combustion zone,substantially completely roasting the coarse ore in the combustion zonein a bed roasting operation while substantially completely roasting thenes in gaseous suspension in the said combustion chamber, therebyproducing sulfur dioxide gas and metal oxide cinder, and withdrawingsulfur dioxide gas from the combustion zone.

6. The method of roasting metal sulfide smalls containing coarse sulfideore and sulde fines which comprises separating the coarse ore and thelines, separately introducing the coarse ore and the fines into acombustion zone, introducing the fines into the combustion zone so as toform in the combustion zone a suspension of the lnes in oxidizing gas,substantially completely roasting the nes while in suspension in theoxidizing gas thereby producing sulfur dioxide gas and metal oxidecinder and creating high temperatures, forming in the combustion zone abed of the coarse ore, substantially completely roasting the coarse orein the combustion zone, under direct iniluence of the high temperaturesdeveloped by the suspension roasting of the nes and in the absence ofheatother than that developed by roasting of the nes and by roasting ofthe coarse ore, to produce sulfur dioxide gas and metal oxide cinder,and withdrawing sulfur dioxide gas from the combustion zone.

7. In-the roasting of a quantity of metal sulde smalls containing coarseore and sulfidev nes by a method involving bed roasting of the coarseore and suspension roasting of 'the fines, said smalls containing nes inamount such that when roasted in "suspension sufliciently hightemperatures are created to effect simultaneous completion of roastingof the coarse ore, the steps comprising separating the coarse ore andthe fines, separately introducing the coarse ore and the fines into acombustion zone, forming in the combustion zone a suspension of thefines in oxidizing gas, roasting the iines while in suspension in theoxidizing gas thereby producing sulfur dioxide gas and metal oxidecinder and creating high temperatures, forming in the combustion zone abed of the coarse ore, roasting the coarse ore in the said combustionzone, under direct iniiuence ofthe high temperatures developed by thesuspension roasting of the lines, to produce sulfur dioxide gas andmetal oxide cinder, and withdrawing .sulfur dioxide gas from thecombustion zone.

8. In the roasting of a quantity of metal sulde smalls containing coarseore and sulde nes by a method involving bed roasting of the coarse oreand suspension roasting of the fines, said smalls containing nes inamount such that when roasted in suspension sufciently high temperaturesare created to effect simultaneous roasting of the coarse ore, the stepscomprising separating the coarse ore and thenes, introducing the nesinto a combustion zone at a point near the l bottom thereof, roastingthe fines in suspension in oxidizing gas while causing the fines to passupwardly and then downwardly through the combustion zone therebyproducing sulfur dioxide gas and metal oxide cinder and creating hightemperatures, introducing the coarse ore into the combustion zone,forming in the bottom of the combustion zone `a bed of the coarse ore,substantially completely roasting the coarse ore in the said combustionzone, under direct influence of the high temperatures developed by thesuspension roasting of the nes, to produce sulfur dioxide gas and metaloxide cinder, withdrawing sulfur dioxide gas from the top of thecombustion zone, and discharging cinder from the bottom thereof.

9. In the roasting of a quantity of metal sulde smalls containing coarseore and sulde fines by a method involving bed roasting of the coarse oreand suspensionroasting of the fines, said smalls containing nes inamount such that when of the coarse ore, the steps comprising separatingthe coarse ore and the ines, introducing the nes into the periphery of acombustion zone at a point'near the bottom thereof, introducing into thebottom of the combustion zone substantially all of the oxidizing gasneeded in the entire roasting operation, roasting the nes in suspensionin oxidizing gas while causing the nes to pass upwardly and thendownwardly through the combustion zone thereby producing sulfur dioxidegas and metal oxide cinder and creating high temperatures, introducingthe coarse ore into substantially the center of the bottom o1' thecombustion zone and forming in the bottom of the combustion zone a bedof the coarse ore, substantially completely' roasting the coarse ore inthe said combustion zone, under direct iniluence of high temperaturesdeveloped by the suspension roasting of the fines and while slowlyworking the coarse ore particles outwardly toward the periphery of thecombustion zone, to produce sulfur dioxide gas and metal oxide cinder,withdrawing sulfur dioxide gas from the topv o the combustion zone, anddischarging cinder from the lower periphery of the combustion zone.

10. In the roasting of a quantity of metal sulde smalls containingcoarse ore and sulfide nes by a method involving bed roasting of thecoarse ore and suspension roasting of the nes, said' smalls containingfines in amount such that when roasted in suspension sufiiciently highternperatures are created to effect simultaneous roasting of the coarseore, the steps comprising separating the coarse ore and the fines,introducing the nes into a combustionzone, roasting the fines insuspension while passing the Iines through the combustion zoneco-current with a stream of oxidizing gas thereby producing sulfurdioxide gas and metal oxide cinder and creating high temperatures,forming in the combustion zone a bed of the coarse ore, substantial- 1ycompletely roasting the coarse ore in the said combustion zone, underdirect inuence of high temperatures developed by the suspension roastingof the rines, to produce sulfur dioxide gas and metal oxide cinder,.andwithdrawing sulfur dioxide gas from the combustion zone.

11. In the roasting of a quantity of metal sulde smalls containingcoarse ore and sulfide nes by a method involving bed roasting of thecoarse ore and suspension roasting of the fines, said smalls containingnes in amount such that when roasted in suspension suiciently hightemperatures are created to effect simultaneous roasting of the coarseore, the steps comprising separating the coarse ore and the fines,introducing the nes in a direction having an initial horizontalcomponent into the top of a combustion zone, introducing into the top ofthe combustion zone a stream of oxidizing gas in sufficient quantity tosupport oxidation of the nes, roasting the l nes While passing the nesthrough the combustion zone co-current with said stream of oxidizing gastherebyvproducing sulfur dioxide gas and metal oxide cinder and creatinghigh temperatures, introducing the coarse ore into substantially thecenter of the bottom of the combustion zone and forming in the bottom ofthe combustion zone' a bed of the coarse ore, introducing into thebottom of` the combustion zone oxidizing gas in sufiicient quantity tosupport oxidation of the coarse ore, substantially completely roastingthe coarse ore in the said combustion Zone, under direct influence ofhigh temperatures developed by the suspension roasting of the fineswhile slowly working the coarse ore particles outwardly toward theperiphery ofthe combustion zone, to produce sulfur dioxide gas and metaloxide cinder, withdrawing sulfur dioxide gas from the combustion zone ata point near the bottom thereof, and discharging cinder from the lowerperiphery of the combustion zone.

12. The method of -roasting metal sulfide smalls containing coarsesulfide ore and at least about 40% by weight of sulfide nes whichcomprises separating the coarse ore and the nes, introducing the finesinto la combustion zone so as to form in the combustion zone asuspension of the fines in oxidizing gas, substantially completelyroasting the fines while in suspension in the oxidizing gas therebyproducing sulfur dioxide gas and creating high temperatures, forming abed of the coarse ore, substantially completely roasting the coarse ore,under influence of high `temperatures developed by the suspensionroasting of the nes, to produce sulfur dioxide gas, and recoveringsulfur dioxide gas. v

13. The method of roasting metal sulfide smalls containing coarse suldeore and at least fabout 40% by weight of sulfide nes to produce sulfurdioxide which comprises separating the coarse ore and the nes,introducing the nes into a combustion zone at a point near the bottomthereof and so as to form in the combustion zone a suspension of finesin oxidizing gas, roasting the fines in suspension in oxidizing gaswhile causing the fines to pass upwardly and then downwardly through thecombustion zone thereby substantially completely roasting the' nes whilein suspension and producing sulfur dioxide gas and metal oxide cinderand creating high temperatures, introducing the coarse ore into thecombustion zone, forming inthe bottom of the combustion zone a bed ofthe coarse ore, substantially completely roasting the coarse ore in thesaid combustion zone, under direct influence of high temperaturesdeveloped by the suspension roasting of the nes, to produce sulfurdioxide gas and metal oxide cinder, withdrawing sulfur Y dioxide gasfrom the top of the combustion zone and discharging cinder from thebottom thereof.

14. The method of roasting metal sulde smalls containing coarse suldeore and at least about 50% by weight of sulfide lines to produce sulfurdioxide which comprises separating the coarse ore and the nes,introducing the fines in a direction having an initial horizontalcomponent into the top of a combustion zone, introducing into the top ofthe combustion zone a stream of oxidizing gas in quantity sufficient tosupport oxidation of the nes, roasting the nes while passing the nesthrough the combustion zone co-current with said stream of oxidizing gasthereby producing sulfur dioxide and creating high temperatures,introducing the coarse ore into substantially the center of the bottomof the 'combustion zone and forming in the bottom of the combustion zonea bed of the coarse ore, introducing into the bottom ofthe combustionzone oxidizing gas in sufficient quantity to support oxidation ofthecoarse ore, substantially completely roasting the coarse ore in the saidcombustion zone, under direct influence of high temperatures developedby the suspension roasting of the fines while slowly working the coarseore particles outwardly toward the periphery of the combustion zone, toproduce sulfur dioxide and metal oxide cinder, withdrawing sulfurdioxide from the combustion zone at a point near the bottom thereof, anddischarging cinder from the lower periphery of the combustion zone.

15. The method of roasting metal sulfide smalls containing coarsesulfide ore and at least about 50% by weight of sulfide fines to producesulfur dioxide which comprises separating the coarse ore and the nes,introducing the fines into the periphery of a combustion zone at a pointnear the bottom thereof, introducing into the bottom of the combustionzone substantially all of the oxidizing gas needed in the entireroastingoperation, roasting the fines in suspension in oxidizing gaswhile causing the lfines to pass upwardly and then downwardly throughthe combustion zone thereby producing sulfur dioxide gas and metal oxidecinder and creating high temperatures, introducing the coarse ore intosubstantially the bottom of the combustion zone and forming in thebottom of the combustion zone a bed of the coarse ore, substantiallycompletely yroasting the coarse ore in the said combustion zone, underdirect influence of high temperatures developed by the suspensionroasting of the fines and while slowly working the coarse ore particlesoutwardly toward the periphery of the combustion zone, to produce sulfurdioxide gas and metal oxide cinder, withdrawing sulfur dioxide gas fromthe top of the combustion zone, and discharging cinderv from the lowerperiphery of the combustion zone.

EDWINy J. MULLEN.

